1) Field of the Invention
The present invention relates to a technology for fixing images on both sides of a recording medium.
2) Description of the Related Art
When printing matter on both sides of a paper, commonly used approach is to form a toner image on one side of the paper, pass the paper through a fixing device to fix the toner image, reverse the paper, and form a toner image on the other side of the paper. This method has a problem in that sometimes the paper is not conveyed properly to the fixing unit. The causes of this problem are: the direction of the paper conveyance is reversed, and the heat applied to the paper, on which one image has already been fixed, curls the paper.
Japanese Patent Application Laid Open (JP-A) No. Hei 1-209470 discloses an image formation apparatus. In this apparatus, toner images are formed on both sides of the paper and the images on both sides of the paper are fixed in one process. In this apparatus, a first transfer unit transfers a first image formed on a photoreceptor to a transfer belt, the first transfer unit transfers a second image formed on the photoreceptor to one side of a transfer paper, and a second transfer unit transfers the first image on the transfer belt to the other side of the paper. Finally, the two images are fixed in one process.
Conventionally, as toner images are formed on both sides of the paper, a member for guiding the paper in the fixing unit can not be used. However, it is necessary to surely convey the paper to the fixing unit so as to prevent an unfixed image from being blurred due to its conveyance. JP-A No. Hei 10-142869 teaches to provide a spur to convey the paper with the toner images. This prevents the unfixed image from being blurred. However, there is a problem in that the toner gets stick to the spur, and this toner gets stick to the paper and degrades the image quality.